1. Field of the Invention
The present invention relates to a detector provided with a detecting element in a holding member and in which lead wires connected electrically to the detecting element are led out of the holding member.
2. Prior Art
In general, a humidity detector of an air conditioning duct insertion type for measuring the humidity in a room is provided with a humidity sensor. In this humidity sensor, a sensor element is set in a casing in the form of a metallic can, for example, and the detection output of the sensor element is taken out of the casing by means of lead wires.
The can-type humidity sensor is provided with a holder that is composed of a metallic base and metallic header. The base is fitted with the lead wires by means of a hermetic seal for insulation. In assembling the sensor, a sensor chip is mounted on the base, electrodes of the sensor chips and the end portions of the lead wires are connected electrically to one another by means of resin conductors, and thereafter, the header is put on and welded to the base to be packaged.
In some cases, in assembling the can-type humidity sensor, an operator may accidentally touch a moisture-responsive surface of the sensor chip by his/her fingers as he/she mounts the sensor chip on the base. In consequence, sebum on the fingers may possibly adhere to the moisture-responsive surface, thereby lowering the performance of the humidity sensor.
Since the header and the base are welded together after the electrodes and the lead wires are connected to one another by means of the-resin conductors, moreover, heat of the welding may be transmitted to resin conductor bonding portions. Accordingly, there is a possibility of the resin conductors being melted to hinder conduction between the electrodes and the lead wires.
Possibly, moreover, a holding member of the sensor chip may be formed of a plastic material. In this case, however, it is necessary to solder the sensor chip and conducting wires in advance and attach the resulting subassembly to the holding member, in order to prevent the holding member from being deformed by heat that is produced as the sensor chip and the conducting wires are soldered. However, this subassembly, composed of the sensor chip and the conducting wires connected by soldering, is low in mechanical strength. In consequence, the conducting wires may bend or coming off the sensor chip in some subsequent process of assembly. Thus, the operator must be cautious in handing the subassembly, so that the efficiency of assembly operation is very poor.
In an alternative can-type humidity sensor, electrodes and lead wires are normally in direct contact with one another, and a conductive resin is used to surround their junctions to secure electrical connection between them. In this case, however, prolonged use of the humidity sensor sometimes causes the electrodes and the lead wires to move relatively to one another, thereby changing the electrical resistance between their contact surfaces inevitably. In some cases, moreover, the electrical resistance between the contact surfaces may be changed by oxidation of the respective surfaces of the electrodes and the lead wires. Owing to these factors, the output of the conventional humidity sensor tends to change with time.
Conventionally, furthermore, there has been a problem that is attributable to the poor working environment of the humidity sensor. More specifically, air with humidity higher than a certain degree continually flows in air conditioning ducts for a heated indoor swimming pool or greenhouse, the environmental conditions for these ducts are poor. If the aforesaid can-type humidity sensor is subjected to these environmental conditions for a long period of time, the metallic casing or metallic parts surrounding the hermetic seal may be corroded, possibly causing a short circuit.
Although these problems have been described in connection with the can-type humidity sensor by way of example, it is to be understood that a can-type temperature sensor are subject to the same problems.
The object of the present invention is to provide a detector improved in assembling properties and environmental resistance.
In order to achieve the above object, a detector according to the present invention comprises a detecting element having electrodes formed on a base, conducting wires connected individually to the electrodes by means of resin conductors formed of an organic high-molecular resin having an electrically conductive material dispersed therein, and a holding member of an organic high-molecular resin for holding the detecting element and the conducting wires, the holding member having a connecting aperture through which junctions between the electrodes and the conducting wires are exposed.
In assembly operation, the electrodes and the conducting wires are connected to one another through the connecting aperture after the detecting element is incorporated into the plastic holding member. Accordingly, the junctions between the electrodes and the conducting wires can be prevented from being broken during the assembly operation.
Since the electrodes and the conducting wires are connected to one another in a manner such that the resin conductors are applied through the connecting aperture after the detecting element is set in the holding member, moreover, the assembly operation involves no high-temperature operation such as soldering. Thus, the holding member, formed of the organic high-molecular resin, cannot be adversely affected by high temperature.
Another detector according to the invention comprises a detecting element having electrodes formed on a base, conducting wires connected individually to the electrodes by means of resin conductors formed of an organic high-molecular resin having an electrically conductive material dispersed therein, and a holding member of an organic high-molecular resin for holding the detecting element and the conducting wires, the electrodes and the conducting wires being kept at a given space from one another.
If the electrodes of the detecting element and the lead wires are brought directly into contact with one another for electrical conduction, the value of contact resistance varies substantially. In the detector of the invention, however, the electrodes of the detecting element and the lead wires are kept at the given space and are connected electrically to one another by means of the resin conductors. In consequence, the variation of the contact resistance value is lessened, so that the detection characteristics of the detector can be kept constant.
In the detector of the invention, moreover, the resin conductors having some elasticity are interposed between the electrodes and the resin conductors. In consequence, the value of contact resistance between the electrodes of the detecting element and the lead wires can be prevented from being changed with time by vibration during prolonged use of the detector.
Preferably, in the detector of the invention, the holding member is formed having a loading aperture through which the detecting element is inserted slidingly.
An operator can assemble the detector without unduly touching the detecting element with his/her fingers, so that the yield of assembly of the detector is improved.
Preferably, in the detector of the invention, the holding member is formed having an elastically deformable retaining portion for holding the detecting element.
Owing to the latching action of the retaining portion, the detecting element can be held securely in the holding member.
Preferably, in the detector of the invention, the conducting wires are molded integrally with the holding member.
In assembling the detector, the lead wires need not be inserted into the holding member, so that the assembling properties are improved. Further, the electrodes of the detecting element and the lead wires can be fixedly spaced when the detecting element is held in the holding member. Thus, the value of resistance between the electrodes and the lead wires conductors can be kept constant individually, so that the properties of the detecting element can be stabilized.
Preferably, in the detector of the invention, the holding member is formed having a hole through which the lead wires are inserted.
Since the lead wires need not be molded integrally with the holding member in advance, the molding cost can be lowered.
Preferably, in the detector of the invention, the holding member is formed having a ventilation aperture through which the detecting element is exposed to the outside air, and the holding member is formed having a protecting portion of the detecting element between the ventilation aperture and the connecting aperture.
This arrangement facilitates the maintenance of the quality of the detector, e.g., a humidity sensor, in which communication with the outside air is essential to the improvement of its detection characteristics and the detection characteristics lower considerably if the detecting element is touched by fingers.
Preferably, in the detector of the invention, the holding member is provided with a closing member for closing the connecting aperture.
In the case of a detector such as a temperature sensor that never strictly requires communication with the outside air, the assembly of the detector can be facilitated by closing the connecting aperture with the closing member, and the detecting element can be protected securely after the detector is assembled.
Preferably, in the detector of the invention, the ventilation aperture and the connecting aperture are covered by means of a porous filter.
With this arrangement, communication with the outside air can be secured to improve the detection characteristics, and the detecting element itself can be protected against waterdrops, dust, etc.
Preferably, in the detector of the invention, air passages capable of facilitating ventilation between the front and rear faces of the detecting element are defined between the detecting element and the holding member.
The detection response can be enhanced by improving the ventilation around the detecting element.
Preferably, in the detector of the invention, the holding member is formed having a push-up portion for keeping the detecting element at a fixed height level above the surface of the base on which the detector is mounted.
Since the detecting element can always be mounted at the fixed height level above the base surface, it never fails to be located in an optimum measuring position.
Preferably, in the detector of the invention, the detecting element is formed having a moisture-responsive surface for humidity detection on one side face thereof, and each of the conducting wires has one end conducting to the electrode on one side face of the detecting element and the other end led out of the holding member so as to extend substantially flush with the other side face of the detecting element.
Out of the electrodes of the detecting element, the electrode on the front or upper side is connected to the ground on the circuit, so that static electricity can be discharged from the upper electrode through the conducting wire on the ground side if it is externally discharged toward the detector. In consequence, high voltage cannot be applied to the moisture-responsive surface, so that the detecting element itself cannot be adversely affected.
Preferably, in the detector of the invention, a projection capable of preventing the holding member from falling down when the holding member is mounted on the base with the wire outlet surface in contact with the base is formed flush with the wire outlet surface.
In the case where the detector is mounted upright on the base surface, the projection can prevent the detector and the lead wires from being leveled on the base surface or broken by external force or vibration. Further, the projection serves to position the detector as the detector is mounted on the base surface.
Preferably, in the detector of the invention, the conducting wires include two lead wires attached substantially parallel to the holding member, the pitch between extending portions of the lead wires extending from the holding member being different from the pitch between resin conductor bonding portions of the lead wires.
The pitch between the resin conductor bonding portions of the lead wires can be adjusted to facilitate the attachment of the resin conductors without being restricted by the pitch between the extending portions of the lead wires from the holding member.